A solid electrolytic capacitor has been developed in which a porous body made of valve-action metal such as tantalum or aluminum is subjected to anodizing process so that a dielectric oxidation film is formed on the porous body and, then, a electrically conductive polymer layer is formed on the dielectric oxidation film, and the electrically conductive polymer layer is employed as the solid electrolyte of the capacitor.
A method of forming the electrically conductive polymer layer which serves as the solid electrolyte of the capacitor is mainly classified into chemical oxidation polymerization or electrolysis polymerization. The monomers of which the electrically conductive polymer material is composed are known to include pyrrole, thiophene, 3,4-ethylenedioxythiopene, and aniline.
Such solid electrolytic capacitors have lower ESR (Equivalent Series Resistance) than a conventional capacitor employing manganese dioxide as the solid electrolyte and, thus, begins to be utilized in various purposes. Recently, as integrated circuits tend to operate at high frequency and large current, a solid electrolytic capacitor has been in demand which has lower ESR and large capacitance and small loss.
As the technique related to such solid electrolytic capacitors, Patent document 1 discloses the improved process for producing the solid electrolytic capacitor with low ESR in which a high-density polymer outer layer with good covering of the edges can be simply achieved and reliably reproduced, comprising the steps of: applying a dispersion a) comprising particles b) of an electrically conductive polymer which comprises polyaniline and/or polythiophene onto a capacitor body which comprises a porous electrode body made of electrode material, a dielectric covering the surface of the electrode material, and a solid electrolyte comprising a electrically conductive material on the dielectric surface; and at least partly removing a dispersing agent d) and/or curing a binder c) in order to form an electrically conductive polymeric outer layer; wherein the particles b) of the electrically conductive polymer in the dispersion a) have an average diameter of 70 to 500 nm
It is preferable that the dispersion a) further comprises a compound including an ether, lactone, amide or lactam group; a sulfone; a sulfoxide; a sugar; a sugar derivative; a sugar alcohol; a furan derivative; and/or a di- or poly-alcohol in order to increase the conductivity.